1. Field of the Invention
This invention relates to a carrier sheet and an original reading apparatus and particularly to a carrier sheet for original feeding used in an original reading apparatus such as a scanner of the sheet-through type or a facsimile apparatus to hold an original, for example, between a lower sheet and a transparent upper sheet, and an original feeding device.
2. Related Background Art
A carrier sheet according to the prior art, as shown in FIG. 21 of the accompanying drawings, has an opaque lower sheet 1 and a transparent upper sheet 2 both made of plastic or like material, and these upper and lower sheets have had their leading end portions in the direction of advance of an original adhesively secured to each other as by welding. In this manner, a thin string-like adhesively secured portion 3 has been formed on the leading end portion of the carrier sheet. The thus constructed carrier sheet is inserted from the leading end thereof in the direction of advance of an original G, i.e., the adhesive securing margin side, into a reading apparatus such as a scanner with the original G sandwiched between the lower sheet 1 and the upper sheet 2, and the reading of the original is effected.
However, the prior-art carrier sheet shown in FIG. 21 has suffered from the following disadvantages when reading is effected by a serial scanner. When an original of thick paper such as a postcard with a photograph held by and between a drive roller 11 and a pinch roller 12 is to be conveyed, the upper sheet 2 and the lower sheet 1 deviate relative to each other to thereby create a level difference in the shape of the thick paper, as shown in FIG. 22 of the accompanying drawings, and in the case of a printer in which the diameters of the drive roller 11 and pinch roller 12 are small, the level difference portion did not nip into the roller and the original could sometimes not be conveyed while slipping.
Also, when the conveying operation further continues with the original slipping, only the upper sheet 2 lying on the drive roller 11 side on which the conveying force works may be fed much as shown in FIG. 23 of the accompanying drawings, and the carrier sheet has rubbed against a scanner head 21 to thereby cause bad conveyance. Further, by the upper sheet 2 and the lower sheet 1 deviating relative to each other, an air layer has been formed between the original and the sheet to bring about a slippery state, and the thick paper such as the postcard with a photograph so that the carrier sheet has deviated relative to each other. Thus, only the carrier sheet has been conveyed and the thick paper such as the postcard with a photograph has not been conveyed with the aforementioned level difference portion being not bitten by the rollers. Therefore, originals which can be conveyed have been limited to a certain degree.
Also, when the carrier sheet is held by and between the drive roller 11 and the pinch roller 12, the amount of conveyance on the drive roller 11 side is greater than that of the pinch roller 12 side. Therefore, the upper sheet 2 and lower sheet 1 of the carrier sheet deviate relative to each other and become downwardly curved as shown in FIG. 24 of the accompanying drawings, and the original reading distance from the scanner head 21 is liable to change or bad conveyance is liable to occur.